Animals held in tanks, pens or cages may be captive, but that doesn't mean they're contained, as was demonstrated in 2010 at SeaWorld. The tragedy wasn't the only time a captive animal turned on its handler.

Lions may thrill audiences at the circus, but they also occasionally threaten their trainers. |
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Working with an apex predator that kills even when it's not hunting means taking a risk means no matter how docile the animal appears to be. Lions can be trained, but they can never really be tame.

A staple of circuses, lion tamers dazzle audiences by prodding the big cats to perform. Occasionally, the lions will turn, however. In 2010, two lions turned on their trainer, Oleksie Pinko, during a show performed before a crowd of hundreds in Lviv, Ukraine. Pinko walked away with minor injuries.

Sigfried and Roy appear with a white tiger cub years after the performance that would end their show. |
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No matter how many years a performer working with exotic animals, a wild creature can still be unpredictable and aggressive.

Roy Horn, of the duo Siegfried & Roy, worked with tigers most of his life, his passion for almost 40 years. In 2003, however, a 7-year-old white tiger named Montecore brought that career to an end when he mauled Horn, seizing upon Horn's neck before being separated by the show's crew.

Ligers exhibit characteristics of both lions and tigers, including their propensity toward aggression. |
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Ligers are half-lion, half-tiger. Given their parentage, it should come as no surprise that these animals are deadly, even when their needs are handled by humans.

In 2008, a liger at Safari's Animal Sanctuary in Broken Arrow, Okla., killed a volunteer, 32-year-old Peter Getz. While Getz was feeding the animal, the liger mauled Getz, attacked his neck and torso. Sanctuary personnel were able to separate the liger from Getz, giving Getz a chance to get out of the cage. But the damage had been done.

Big cats aren't the only potential killers in captivity. Bears may also turn on their trainers.

In 2008, a trainer bear that was featured in the movie "Semi Pro" attacked and killed 39-year-old Stephan Miller with a single bite to the neck. According ABC News, Miller was the cousin of famed animal trainer Randy Miller, who had previously described the animal as "the best working bear in the business." He also cautioned of the bear's violent potential.

Bears won't just attack humans, but also potentially other animals that are unfortunate enough to be placed alongside this giant predators. In an ugly stunt that played out at the Shanghai Wild Animal Park in China, a bear mauled a monkey to death during a bike riding race, a skill both had been trained to perform. When they crashed, the bear killed the small monkey before trainers could separate them. The park had a history of animal abuse allegations.

Travis the chimp met a bloody end after the attack on Charla Nash. |
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In a gruesome case that shocked a nation with its brutality, a trained chimpanzee named Travis, who had previously made television appearances, mutilated a woman, Charla Nash, in the home of his owners in Stamford, Conn.

The attack wasn't the first time that Travis showed aggression, but it was undoubtedly the most violent. Nash lost her eyes, hands and most of her face in the attack, forced to undergo many rounds of surgery, including a facial reconstructive procedure.

During the attack, Travis was stabbed by one of his owners in an attempt to pry him off Nash. When officers later arrived on the scene, they shot and killed the ape. Lab tests after the attack showed that Travis's owners had given him tea laced with Xanax in an effort to calm him down earlier that day.

An elephant can do a lot of damage, even when it doesn't mean to. |
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If there's any animal that can unleash serious damage, even when it doesn't mean to, it's the elephant.

The Elephant Sanctuary in Hohenwald, Tenn., saw tragedy in 2006 when a trainer was killed while tending to an elephant named Winkie. Thirty-six-year-old Joanna Burke was examining a swollen eyelid thought to be caused by an insect bite. Winkie abruptly spun around as Burke approached his side, knocking her across the face and chest. He then took one step too many, and crushed Burke who was lying on the ground, killing her instantly.

The death was ruled an accident following an investigation by the Tennessee Wildlife Resources Agency and the Sheriff's Department, and Winkie was allowed to stay at the park.

When reacting to fear, horses can be aggressive and dangerous. |
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Horses are large, fast, powerful animals that have lived alongside humans for millennia. Despite our long-standing relationship with them, horses do still turn on their handlers, occasionally with deadly consequences.